This invention relates generally to the field of straw bale construction and more specifically to a vent that is incorporated into the wall joinery system between the bottom of a straw bale wall and the top of its"" foundation to allow condensation from within the wall to be removed.
Straw bale construction is a technique for building structures that greatly reduces and in some instances can even eliminate the use of lumber by forming walls out of stacked straw bales. The resurgence of straw bale construction has introduced current knowledge about modern materials and construction analysis to create structures that are especially durable and energy efficient when compared to both traditional lumber and non-lumber built structures. For example, modem straw bale construction features steel rebar that is driven through the straw bales that form the walls in order to provide strength, rather than more traditional materials such as bamboo or lumber. In addition, cables can be wrapped from the foundation to the roof-plate to form an exoskeleton. Modern straw bale construction also takes advantage of computer simulation and other techniques presently adapted to building construction to optimize designs for improved energy efficiency, for example.
The greatest strengths of straw bale construction are the fact that it is using a waste product as a building material and that wall structures having insulation values from r50-r60 are possible. These two factors make this construction medium an extremely promising component for addressing the global energy situation. However, there are several places where this technique needs refinements.
One involves the most vulnerable point of straw bale construction, namely moisture that tends. to collect in the lower outside corner of the wall. Therefore, the need exists for a vent system incorporated into the wall joinery system between the bales and the foundation in order to increase the longevity of straw bale wall systems. When kept dry, bales have been shown to last in excess of 100 years.
Straw bale construction combines well with other building technologies like greenhouses and cob for thermal mass. As a result, structures that combine the advantages of several natural building techniques are facilitated by straw balexe2x80x94allowing designs of maximum diversity, efficiency, and comfort.
These four advantages make straw bale special with respect to the following environmental considerations: 1) Reduced lumber consumption, 2) Increased thermal efficiency, 3) Use of a waste product as a building material, and 4) Adaptability to other building technologies. Clearly, a system that would increase the longevity of straw bale wall systems would further advance these environmental factors.
As shown in FIG. 1, straw bale structures typically include a cement foundation 10 and a wall 12 disposed thereon. The wall 12 is built of a plurality of straw bales 14 held in place by a plurality of steel rebar 16. The rebar 16 between a first row 18 of straw bales 14 and the foundation 10 is set in the foundation 10 while the cement is still wet. Thereafter, the first row 18 of straw bales 14 is set in place such that each bale 14 is impaled onto rebar 16 protruding from the foundation 10. FIG. 1 includes a partial cut-away section to show several rebar 16 set into the foundation 10 and protruding up into a straw bale 14. A new set of rebar 16 is then driven into the first row 18 of bales 14 such that approximately half of the length of each rebar 16 protrudes out of the bales 14. A next row of bales 14 is then impaled on the rebar 16 and the process is repeated. It will be apparent to one skilled in the art that this technique can be varied in many ways including the offset of the bales 14 from one row to the next as well as in terms of the number of rebar 16 used per bale 14, the particular arrangement of rebar 16, and how that arrangement is offset between adjacent rows of bales 14.
As shown in FIG. 2 a typical straw bale wall 12 includes both an interior siding 20 and an exterior siding 22. The interior siding 20 is commonly formed of plaster and is provided to prevent straw and straw dust from contaminating the interior of the structure, to provide a preferred surface for painting and anchoring fixtures, and to improve the insulation value of the wall 12. The exterior siding 22 is commonly formed of stucco and is provided to prevent the bales 14 from degrading due to sun, rain, and wind, to provide a preferred surface for painting and anchoring fixtures, and to improve the insulation value of the wall 12. An interfacial layer (not shown) is provided on both sides of the wall 12 to improve the adherence of sidings 20, 22. Interfacial layer 24 is commonly chicken wire.
Straw bale walls 12 have proven to be strong and durable, and have excellent insulating properties. However, it has also been found that warm, moist air from within the structure can penetrate the plaster of the interior siding 20. This can cause condensation 23 to form on an interior surface 24 of the exterior siding 22. The condensation 23 then tends to drip down the interior surface 24 and pool at the bottom along the foundation 10, as shown in FIG. 2, and can cause the straw to rot.
Accordingly, what is desired is a venting system that can be interposed between the wall 12 and the foundation 10 to collect moisture and to vent it back into the interior of the structure without significantly increasing building costs and without significantly diminishing the insulation value of the wall 12.
According to an embodiment of the present invention, a straw bale wall vent box comprises a lower member, a substantially planar top member, and a plurality of rebar disposed through the top member and the bottom side of the lower member. The lower member includes substantially parallel first and second sides, an exterior side, and an optional bottom side. The top member is substantially planar and includes a plurality of apertures, and can further include a stucco screed on an exterior end and a plaster screed on an interior end. The top member is disposed above and substantially parallel to the bottom side of the lower member, and is joined to a top edge of the exterior side of the lower member. The plurality of rebar is disposed through the top member and the bottom side of the lower member. This structure is advantageous as the apertures allow moisture from the straw bales to enter the vent box from which it can then vent into the air space above the foundation. The rebar serves to transfer the load from the top member to the foundation.
It will be appreciated that although the embodiments described herein and shown in the drawings all include stucco and plaster screeds, these are not critical elements to the invention and in some simple embodiments they are excluded. One of skill in the art will readily see how the invention can be constructed and used without screeds, or with only an exterior or interior screed.
The lower member can further include a drainage floor sloping downwardly from the exterior side, the rebar being disposed through the drainage floor. In those embodiments that include a drainage floor the bottom side is optional. The lower member can also include a trim piece substantially parallel to the exterior side and extending from the bottom side towards the plaster screed. The trim piece in some embodiments joins the plaster screed. In some embodiments the drainage floor joins the trim piece along its top edge, and in other embodiments along a line beneath and substantially parallel to the top edge. The drainage floor is advantageous to guide moisture towards the interior side of the vent box. In those embodiments in which the drainage floor joins the trim piece along its top edge, moisture can drain out of the vent box. In those embodiments in which the drainage floor joins the trim piece beneath the top edge, the moisture will tend to evaporate and vent out of the box through the opening between the top edge of the trim piece and the plaster screed.
In those embodiments in which the trim piece joins the plaster screed, the first and second sides of the lower member each can include at least one aperture. In those embodiments that include a drainage floor, the apertures in the first and second sides are disposed above the line along which the drainage floor joins the two sides. In other embodiments in which the trim piece joins the plaster screed, the first and second sides of the lower member are each bounded by the bottom side, the exterior side, and the drainage floor. In each of these embodiments the advantage of either apertures or first and second sides that do not extend beyond the drainage floor is to provide for air circulation between adjoining vent boxes when configured as a straw bale wall vent system as will be described in greater detail below.
Some embodiments include insulation within the bottom portion of the lower member. The insulation is advantageous to insulate against the cold of the foundation. In some of these embodiments a space within the lower member is defined by the bottom side, the drainage floor, the exterior side, and the first and second sides, and this space includes an insulation. However, in those embodiments that do not include a drainage floor the insulation can simply form a layer on the bottom side of the lower member.
Additional embodiments of the present invention are directed to a straw bale wall vent system comprising a plurality of wall vent boxes, as previously described, wherein the plurality of wall vent boxes are placed side by side so that the first and second sides of adjacent vent boxes are substantially in contact. In those embodiments in which each vent box includes a trim piece that extends upwardly to join the plaster screed, the plurality of adjoining vent boxes essentially forms a tube. Therefore, to provide air circulation necessary to remove excess moisture, the system further includes an air blower configured to force air into one of the vent boxes, and an outlet in one of the vent boxes through which the air may escape.
These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following descriptions of the invention and a study of the several figures of the drawings.